1. Field of the Invention
The disclosure generally relates to the oil and gas industry. More particularly, the disclosure relates to chokes for the oil and gas industry.
2. Description of the Related Art
A type of flow control known in the oil and gas industry as a “choke” adjustably controls a through-flow of production fluids in pipes and other tubing. Chokes are typically located in proximity to a well to control production fluids from the well. Manually adjustable chokes have been used for decades, and typically have an adjustable hand wheel that can rotate a threaded shaft and move a tapered stem in and out of a choke seat to vary the available flow area and thus the flow.
One of the sources of overpressure conditions in a choke is caused by field use of the choke in unintended ways. The typical choke is not designed or intended to operate as a closing valve. However, field crews can and do entirely close the choke with the stem (or a plug coupled to the stem) against the seat. The force required to linearly close the stem against the seat can break the stem, rendering the choke useless until repaired. Some manufacturers include a shear pin at some position along the stem, so that the shear pin breaks before the stem, but still renders the choke useless until repaired.
As the industry progressed, motors, typically hydraulic motors, began to actuate chokes. One of the challenges in the motor actuated chokes is the ability to move the threaded stem (or a threaded shaft coupled to the stem) and then lock the stem into position, so that an overpressure burst of production fluid does not change the position of the stem relative to the seat. One improvement in the industry is attaching a worm gear transverse to a threaded shaft that is coupled to the stem to help hold the stem in position, but such improvement has only been partially successful, and some chokes can fail with overpressure conditions. When the choke is used undesirably as a closing valve, sometimes downstream pressure can surge unintentionally and cause backpressure in the choke components exposed to the downstream pressure. The construction in the downstream components results in a much larger square area than the upstream pressure area between the stem and seat. The pressure on the downstream components applied over the larger pressure area creates a much larger force than would have occurred on the upstream components with the smaller square area, and the choke can fail, internally and externally, and even break apart.
Thus, there remains a need for providing a design for a choke with an improved actuator assembly.